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When the vibration head dipped into the middle of the melton, the better grain refinement effect can be gotten.
It has been reported that ultrasonic vibration can generate a high number density of fine ice crystals in the solidification of water within a short time[4].
These grain refinement of the microstructures by the UV technique also have been observed in other alloys.
The grain size of Fig.2(b) is smaller than that of Fig.2 (a), especially at the bottom of the ingots.
It can be seen form Fig.2 (a) that microstructure is coarse columnar grain and the grain size is not very uniform.

This mechanism involved the disappearance of low angle grain boundaries, which gave rise to the onset of a local grain coalescence mechanism that clusters grains that were only separated by low angle grain boundaries.
Chen et al. [14] observed that usually a small number of Goss grains grow during the early stages of secondary recrystallization.
It appears from these figures that disappearing low angle grain boundaries have a large impact on the nucleation of abnormal grain growth, although all theories of grain growth agree on the complete immobility of these grain boundaries.
As a large number of similarly oriented grains nucleate during primary recrystallization in one single deformation band of the deformed microstructure, it automatically produces the contiguous strings of grains that are only separated by low angle grain boundaries.
This gives rise to the clustering of grains that produces the long elongated grains at the onset of abnormal grain growth.

During certain number of passes (six passes), the material experiences higher hardness with fair amount of ductility.
Stress Vs strain graph With further straining (increasing number of passes), these dislocations aid to form dislocation cells/sub grains, resulting in grain refinement and strength enhancement.
This grain refinement is due to the evolution of sub grains within big grain (bimodal structure).
In addition, grains are sheared resulting in oblate grain structure, with grain axis inclined to the extrusion direction.
With increasing number of passes, the material experiences a critical strain and there by obtains an oblate grain structure, which is associated with high angle grain boundaries and leads to enhancement of strength with reasonable ductility 3.

The SD grains and the SDC grains coated with Ti are selected.
The setting rate of SDC grains is larger than that of SD grains, and setting position accuracy of SDC grain array is better than SD grain array.
SD grains begin to jump at about 20ms in applying voltage time and jumping rate, i.e. number of jumping grain, increases gradually and unstably with an increase of applying voltage time.
The distribution in grain distance of SDC grains is narrower around 1mm in grain distance rather than SD grains.
(4) The setting grain positioning accuracy of SDC grain is better than that of SD grain.

For GAM a grain definition is needed.
A grain is defined by an area boundary by a continuous boundary above 5° misorientation: GAM representing average point-to-point misorientation inside such a grain.
Seshadri, Relative effect(s) of texture and grain size on magnetic properties in a low silicon non-grain oriented electrical steel, Journal of Magnetism and Magnetic Materials 264 (2003) 75–85 [2] Chikara Kaido, Spiral core made of grain-oriented electrical steel sheet, Electrical engineering in Japan, Vol. 118, No. 3,1997 [3] Yu.
Landgraf, Effect of deformation and annealing on the microstructure and magnetic properties of grain-oriented electrical steels, Journal of Magnetism and Magnetic Materials 304 (2006) e617–e619 [9] Ken-ichi Yamamoto and Yasumasa Yamashiro, Effect of compressive stress on hysteresis loss and magnetostriction of grain oriented Si–Fe sheets, journal of applied physics, volume 93, number 10, 2003 [10] G.
Groma,X-ray line broadening due to an inhomogeneous dislocation distribution, Physical Review B, Volume 57, Number 13

The calculation shows that the maximum number of dislocation emission increases with the increase of applied stress, as shown in Fig. 4, which also illustrates the variation of the maximum number with the grain size .
It is clearly shown that the decrease of the grain size can decrease the value of the maximum number of the dislocation.
It means that void growth can hardly occur for small grain sizes.
The maximum number of edge dislocation emitted from the surface of nanovoid as a function of grain size in nanocrystalline materials.
The void growth depends on the applied remote stress and the grain size.

It was found that addition of Ti at this level resulted in grain refinement of aluminum structure whereas addition of Zr alone resulted in grain coarsening of Al structure while it resulted in grain refinement when it is added in the presence of Ti.
As mentioned before Zr, Ta and Cr have a poisoning effect, i.e. the grains become larger when the grain refiner is added or reducing the grain refining efficiency of Al-Ti and Al-Ti-B master alloys.
Determination of the Wear of Aluminum and its Microalloys The basis of wear theories was attempted to explain the wear process on a microscopic scale and to relate the magnitude of the wear to the material properties, and to the number and nature of the local encounters.
The first such theory was proposed which related the wear rate to the number of interatomic encounters between the opposing surfaces [11].
Addition of Ti resulted in grain refinement of commercially pure aluminum whereas addition of Zr resulted in grain coarsening.

The combination of diffraction and extinction information aids the grain indexing operation, in which pairs of diffraction and extinction images are assigned to grain sets. 3D grain shapes are determined by algebraic reconstruction from the limited number of extinction projections, while crystallographic orientation is found from the diffraction geometry.
To extract all the information contained in such an image, a number of data processing steps are required.
A number of criteria are used to achieve this.
By exploiting both extinction and diffraction spots during the data analysis the grain indexing algorithm is simplified, allowing large numbers of grains to be successfully treated.
In future, it is hoped that improvements can be made to the algorithm to allow samples with even larger numbers of grains (>1000) to be mapped, and to accommodate samples with greater levels of mosaicity than can be handled at present.

As a result, ultra fine-grained austenitic single structure with the grain size of about 0.6µm was obtained.
Then, it was concluded that the tensile properties markedly deteriorate when the number of grains existing in the diameter direction becomes smaller than about 5.
Tensile Properties of Ultra Fine-Grained Wire.
However, the proof stress of the ultra fine-grained thin wire is comparable to that of bulk material which has the identical grain size.
This is due to the fact that the number of grains existing in the diameter direction becomes much larger than 5 by ultra grain refinement, although the wire is very thin.

The mathematical models that can be used to describe cutting by lapping need to take into account the shape of the abrasive grain, the modality of material removal, the number of grains in contact etc. [3].
By the repeated action of numerous abrasive grains the number of cracks grows, they deepen and overlap thus generating the material removing erosion process [6], [7].
Dependence of grain penetration depth on grain dimensions Only the large abrasive grains participate in cutting the workpiece surface, namely particles with dimensions falling into the interval [δ; dmax].
Fig. 7 presents the case of lapping with a F400 micropowder (micro grains) F400, with an average abrasive grain dimension of dmed = 17.3 ± 1 µm.
(14) Of the total of abrasive grains only fraction Fp participates in cutting, hence the volume of the effectively cutting grains is: